<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        // var age = prompt('请输入你的出生年份');
        // var year = 2021 - Number(age);
        // alert('你的年龄是'+ year + '岁');
        var number1 = prompt('请输入第一个值');
        var number2 = prompt('请输入第二个值');
        var sum = Number(number1) + Number(number2);
        alert('两个值之间的和是:' + sum);
        alert(number1 - -number2)
    </script>
</body>
</html>